Python3入门：从基础到函数，全面教程

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本资源是一本名为《The Art and Craft of Programming Python Edition》的入门教材，由John C. Lusth编写，出版日期为2014年2月27日。这本书主要针对Python 3语言，特别适合初学者学习。以下是部分章节内容概要： 1. **开始入门**： - 章节介绍如何运行Python程序，包括安装环境设置和基本命令行操作，为后续学习奠定基础。 2. **基本数据类型**： - **整数(integers)**：讲解了整数的表示和基本运算。 - **实数(real numbers)**：介绍了浮点数和复数的概念。 - **字符串(strings)**：涵盖字符串的定义、操作和处理。 - **布尔值、None和集合(collections)**：解释了True、False和None这些基本逻辑值，以及列表、元组和集合等数据结构。 3. **组合和运算**： - **数值运算(numeric operators)**：介绍了算术、关系和位运算符。 - **比较(comparing things)**：如何使用比较运算符进行比较。 - **复合比较(combining comparisons)**：讨论了如何组合多个条件进行复杂判断。 4. **运算符优先级与结合性**： - **运算符优先级(precedence)**：说明了Python中的运算符顺序，以确保正确执行表达式。 - **运算符结合性(associativity)**：探讨了如何理解左到右或右到左的运算符结合规则。 5. **变量和赋值**： - **变量(variables)**：讲解变量的作用、声明和数据类型。 - **变量命名(variablenaming)**：强调了命名规则和最佳实践。 - **赋值(assignment)**：包括不同赋值模式，如转移、更新、丢弃等，以及函数调用中的赋值行为。 6. **条件语句**： - **逻辑表达式(logical expressions)**：介绍了布尔表达式的构造。 - **逻辑运算符(logical operators)**：如AND、OR、NOT等的使用。 - **短路逻辑(short-circuiting)**：讨论了在条件判断中的逻辑非空检查。 - **if-elif-else**：讲解了多条件分支的结构。 7. **函数(functions)**： - **封装功能(Encapsulating operations)**：阐述了函数的作用，如何将一组相关操作打包成可重用单元。这本书通过逐步深入的方式，让读者掌握Python 3语言的基础语法和逻辑结构，为后续编程实践打下坚实的基础。无论是初次接触编程还是希望提升Python技能的读者，这都是一本值得参考的入门教材。

16 CHAPTER 2. LITERALS

Chapter 3

Combining Lit era l s

Like the literals th em sel ves, combinations of literals are also expressions. For example, suppose you have

forgotten your times table and aren’t quite sure whether 8 times 7 is 54 or 56. We can ask Python, presenting

the interpreter w it h the expression:

>>> 8 * 7

>>> 8*7

Pressing the Enter key signals the end of the expression. The multiplication sign * is known as an operator, as

it operates on the 8 and the 7, producing an equivalent literal value. The 8 and t he 7 are known as operands.

It seems that the actual names of variou s operands are not being taught anymore, so for nostal gi a’ s sake, here

they are . The operand to the left of the multiplication sign (in this case the 8) is known as the multiplicand.

The operand to the right (in this cas e the 7) is known as the multiplier. The resu lt is known as t he product.

The operands of the other basic operators have sp e ci al names too. For addition, the left op e r and is known as

the augend and the right operand is known as the addend. The result is known as the sum. For subtraction,

the left operand is the minuend, the right the subtrahend, and the result as the di↵erence. For division (and

I think this is still taught), the left operand is the dividend, the right operand is t h e divisor, and the resul t

is the quotient. Finally, for exponentiation, which is shorthand for repeated multiplication:

>>> 3 ** 4

>>> 3 * 3 * 3 * 3

the lef t operand is the base and the right ope r and is the exponent.

In general, we will separate operators from their operands by spaces, tabs, or newlines, collectively known

as whitespace.

It’s not necessary to do so, but it makes your code easi er to read.

Python always takes in an expression and displays an equivalent lite ral expres si on (e.g., integer or real). All

Python oper ator s are binary, meaning t h ey operate on exactly two operands. We ﬁrst look at the numeric

operators.

Computer Scientists, when they have to write their annual reports, often refer to the things they are rep orting on as

darkspace.It’salwaysgoodtohavealotofdarkspaceinyourannualreport!

3.2. COMPARING THINGS 19

Subtraction and division of numb e r s follow t he same rules as addition. However, these operators, as deﬁned,

do not work for strings and arrays.

Of special note is the division operator with respect to integer operands. Consider evaluating the fol l owing

expression:

15 / 2

If one asked the Python i nterpreter to perfor m this task, the result would be 7.5, as expected. However,

often we w is h for just the quotient without the remainder. In this case, the qu ot ie nt is 7 and the remainder

is 0.5. The double forward slash ope r ator is P y th on ’s quotient operator; if we ask the interpreter to evaluate

14 // 5

the resu l t would be 2, not 2.8. Use of the quotient operator is known as integer division.

The complement to integer division is the modul us operator %. While the result of integer division is the

quotient, the res ul t of the modulus operator is the remainder. Thus

14 % 5

evaluates to 4 si n ce 4 is left over when 5 is divided into 14. To check if this is true, one can ask the interpreter

to evalu at e:

(14 // 5 * 5) + (14 % 5) == 14

This complicated expression asks the question “is it true that the quotient times the divisor plus the remainder

is equal to the original divi d en d? ”. The Python interpreter will respond that, indeed, it is true. The reason

for th e parentheses is delineate the quotient and the remainder within the addition. The parentheses can

also be used to change the precedence of operat or s; this is is explained in more detail in the next chapter.

3.2 Comparing thi ngs

Remember the Boolean literals, True and False? We can use the Boolean comparison oper at or s to

generate s uch values. For example , we can ask if 3 is l e s s than 4:

>>> 3 < 4

True

The interpreters re sponse says that, indeed, 3 is less than 4. If it were not, the interpreter would re spond

with False.Besides< (less than), there are other Boolean comparison operators: <= (less than or equal

to), > (greater than), >= (greater than or equal to), == (equal to), and != (not equal to).

Note that two equal signs are used to see if to things are the same. A single equals sign is reserved for the

assignment operator, which you will learn about in a later chapter.

Besides integers, we can compare reals with reals, strings with strings, and arrays with arrays using the

comparison operators:

In most other modern programming languages, a single / means integer division, so don’t forget this when you learn a new

language!

20 CHAPTER 3. COMBINING LITERALS

>>> "apple" < "banana"

True

>>> [1, 2, 3] < [1, 2, 4]

True

In general , it is illegal to compare integers or reals with strings.

Any Python type can be compared with any other type with the equality and inequality operators, ==

and !=. These operators are used to see if two things are the same or not the same, as the case may be.

Usually, for two things to be considered the same, they have to be the same kind of thing or type. For

example, the expression: 123 == "123" resolves to False, because integers are not strings and vice versa.

Likewise, "False" != False resolves to True, becau se strings are not Booleans and vice versa. There is

an exception, though. If an integer is compared with a real, the integer is converted into a real before the

comparison is made. In the case of arrays, == will return False if the arrays have di↵ering lengths. If the

arrays have equal length, then each item in one array is compared using == to the resp ec ti ve item in the other

array. All individual items must be equal for the two arrays to be equal. For example [1, [2, 1, 0], 3]

and [1, [2, 1, 8], 3] would be considered “not equal”, since the middle items would not be considered

equal.

3.3 Combining comparisons

We can combine comparisons with the Boolean logical connectives and and or:

>>> 3 < 4 and 4 < 5

True

>>> 3 < 4 or 4 < 5

True

>>> 3 < 4 and 5 < 4

False

>>> 3 < 4 or 5 < 4

True

The ﬁrst interaction asks i f both the expression 3<4and the express ion 4<5are true. Since both are,

the interpreter responds with True. The second interaction asks if at least one of the expressions is true.

Again, the interpreter responds with True.Thedi↵erencebetweenand and or is illustrated in the last two

interactions. Since only one expression is true (th e latter expression being false) on l y the or ope rat or yields

a true value.

There is one more Boolean logic operation, called not. It simply reverses the value of the expression to

which it is attached. The not operator can only be called as a function (since it is not a binary operator).

Since you do not yet know about function s, I’ll show you what it looks like but won’t yet explain its ac ti on s.

>>> not(3 < 4 and 4 < 5)

False

>>> not(3 < 4 or 4 < 5)

False

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